David Wozniak, played by Vince Vaughn, is a well-meaning but unlucky deliveryman working in his family's butcher shop. He finds himself in hot water with thugs due to a debt of $80,000, which he incurred while investing in a company named NewTech, only to see its owner arrested for unrelated issues. His father, Mikolaj (Andrzej Blumenfeld), holds a low opinion of him, adding to David's sense of inadequacy. Together with his brothers, Aleksy (Bobby Moynihan) and Victor (Simon Delaney), they navigate an underwhelming family life.
Things complicate further when David's girlfriend, [Emma](cobie-smulders), portrayed by Cobie Smulders, is pregnant, but their relationship is strained. Emma's dissatisfaction with David grows as he often neglects her, failing to communicate for days on end.
In a bizarre twist, David learns from lawyer Mark Williams (Damian Young) that he is the biological father of 533 children due to his past sperm donations—an unusual twist of fate where the clinic mistakenly utilized his donations for multiple clients. This revelation sparks a class action lawsuit from 142 of those children, eager to uncover the identity of "Starbuck," the pseudonym David used.
To navigate this tangled situation, [Brett](chris-pratt), played by Chris Pratt, serves as David's lawyer and confidant. He provides David with profiles of the children involved in the lawsuit, igniting David's interest in their lives. In a heartwarming turn of events, he discovers that one of his children, Andrew Johansson, is a rising star in the basketball world, which motivates him to extend his support to others.
One such child is [Josh](jack-reynor), a budding actor and bartender who faces challenges in his career. David takes it upon himself to ensure Josh can pursue acting despite losing his job, demonstrating his commitment to being involved in the lives of his biological children.
In another touching episode, David visits a girl named Kristen (Britt Robertson), who is grappling with substance abuse. Instead of allowing her to stay in the hospital, he believes in her potential and signs her release papers, allowing her to take charge of her life again.
David's expanding family and relationships with these children grow deeper, even as David faces pushback from [Brett](chris-pratt), who cautions him about the potential ramifications of interfering in their lives. Complications arise when one of the children, Viggo (Adam Chanler-Berat), learns of David's identity and starts utilizing this to spend more time with him. With media attention focused on the unprecedented number of siblings meeting, David's anonymity is at stake.
As events develop, David increasingly becomes a dedicated partner to Emma and a father to their child. Following a tumultuous encounter with the thugs—ultimately leading to a heightened demand for $100,000—David, with Brett's assistance, decides to sue the sperm bank, eventually winning $200,000 while maintaining his secret identity.
Despite moments of doubt, David comes to terms with his newfound family connections and decides to disclose his identity via Facebook. His life takes another turn when he rushes to Emma’s side as she goes into premature labor. At the hospital, amidst the chaos, he proposes to Emma while all his biological children gather to celebrate this new chapter.
